As thin film electrode materials of semiconductor devices such as DRAM and FERAM, ruthenium or a ruthenium compound is used. Examples of methods for manufacturing a thin film include chemical vapor deposition methods such as a CVD method (chemical vapor phase vapor deposition method) and an ALD method (an atomic layer vapor deposition method). As the raw material compound to be used for such chemical vapor deposition methods, many organic ruthenium compounds have been known conventionally.
A manufacturing cost of thin films using an organic ruthenium compound by a CVD method or the like is based on the use efficiency of the organic ruthenium compound raw material, besides costs for the organic ruthenium compound as the raw material. The use efficiency is a ratio of a compound amount consumed for film formation reaction to the raw material mass which has been introduced into the surface of a substrate, and the use efficiency of the organic ruthenium compound by, for example, the CVD method becomes low, for example, 10% or less in many cases. If problems of the low use efficiency are left unaddressed, a cost for manufacturing a ruthenium thin film, and, in turn, price increase of various devices are caused. In addition, resource exhaustion of ruthenium as noble metal may occur.
Herein, the present applicants have conventionally developed a recycling technique of an organic metal compound, which include extracting unreacted organic metal compounds from a used raw material and purifying them into a reusable state as a method for reducing a film formation cost and avoiding problems of resource exhaustion (e.g., refer to Patent Literature 1). This recycling technique including allowing a raw material gas after thin film formation to pass through, for example, a cold trap, recovering it by cooling and condensing thereof, and further distilling this recovered material under appropriate conditions so as to purify and extract an organic metal compound. According to this recycling technique, it is possible to reduce thin film manufacturing cost by avoiding waste of organic metal compounds.
Furthermore, the present applicants have also found that the organic metal compound recovered as mentioned above has problems of contamination of product by side reaction with respect to film formation reaction or coloring, and it is difficult to remove such problems by purification means such as distillation and that such material cannot be reused as a thin film raw material. Then, the present applicants have also developed a recycling method including purification means for making a recovered organic metal compound into a reusable state (e.g., refer to Patent Literature 2).
The above-mentioned technique for recycling an organic metal compound by the present applicant is applied to many organic ruthenium compounds which are used in development, and has results as to the efficient use thereof. According to the present inventors, however, it is demonstrated that some types of organic ruthenium compounds cannot be made into reusable state even if the above-mentioned conventional purification process is carried out.
In this point, as an organic ruthenium compound for thin film formation, conventionally, it has been required to have a low melting point and being liquid at ordinary temperatures, a high vapor pressure, and being able to be easily vaporized. This makes importance on handling property of the raw material or efficiency at a thin film manufacturing time. However, in recent years, in addition to such properties, compounds corresponding to various reaction atmosphere, and compounds which make more importance on properties of the manufactured thin film have been required, and an organic ruthenium compound in response to this have been developed (e.g., refer to Patent Literature 3). These relatively new organic ruthenium compounds have been made to have more complexity including specificity of ligands to be coordinated, asymmetric property of different ligand to be coordinated, and the like, as compared with conventional one. Thus, from the studies by the present inventors, conventional recycling techniques cannot completely correspond to such relatively new organic ruthenium compounds.